Faulty water cylinder thermostat?

[Harry Bloomfield]

How do I check the boiler output temperature? Isn’t it 60 as shown in the picture? I thought 60 was ok?

The HW setting is on the upper adjustment knob and does appear to be set at 60, but would need to be at least 70C to achieve 60C in the cylinder. The lower one sets the boiler's output temperature for when CH is called for.

However, I suspect you don't actually have a split system - one where boiler's HW output temperature can be set differently to the CH output temperature. Try setting the lower knob up to maximum and report back..

You probably have what's called an 'heat only boiler', which means it only responds to a demand for heat, but doesn't know or care where the demand came from.

 

[stem]

Are you sure that hot water cylinder is still in use?

There are generally two ways of heating hot water with a gas boiler:

1. Is with a combi boiler that is capable of producing hot water instantly when a tap is turned on. The dial with the tap symbol would regulate the temperature of the hot water it delivers. A hot water cylinder is not necessary.

2. Uses a hot water cylinder to store water whilst it is heated by the boiler, Hot water cylinders are usually connected to a system boiler (not a combi) and the boiler simply heats the water in the cylinder where it is stored until required. The thermostat on the cylinder controls the temperature of the stored water.

It is rare, but not unknown, to have a combi boiler hooked up to a hot water cylinder. So, first of all I would ascertain if the hot water cylinder is actually in use. It's quite easy to test. Switch off the central heating and whilst you stand near the boiler get someone to open up the taps one by one for 30 seconds or so. If the boiler fires up every time a tap is opened the boiler is providing the hot water and not the hot water cylinder. Are the cold water storage tanks above the hot water cylinder empty?

 

[Hugh Jaleak]

You have a 'S' plan system, the 2 Honeywell valves control the heating and hot water. Turn the cylinder stat right up, and with CH off, check both pipes under the motorised valves, the boiler and pump should be running and one (I suspect the Right hand 28mm) pipe should be getting hot. If it doesn't, slide the little lever on the top of the valve across in its slot, you should hear the valve 'whirr' as it opens, lock it into the detent and see what happens then. (Check boiler and pump are running, if they're not, you might have to switch the CH on as well).

If the boiler runs without the CH on at this stage, check pipework under valve is getting hot. If so, valve is probably faulty. You can turn boiler temp up as well I think, if cylinder controls are working correctly then contents wont go above the set temp on the cylinder stat.

 

[Mojo12345]

Ok thanks will try also I wanted to ask about insulation my boiler and pipes are in the garage do they need insulation and how to measure the pipe for insulating? Also what type of foam insulation for pipes should I get is Armaflex a good brand ? also does the hot water tank need cylinder jacket for insulation as I don’t have one does it make much difference? Thanks for advice

 

[Hugh Jaleak]

Pipework will be one of 3 sizes, 15mm, 22mm or 28mm. For easy reference, look at the pipework going into the cylinder in the above photo. The 2 pipes coming up to it are 28mm, they reduce to 22mm to go into the cylinder, and the short stub on the top connection, (formerly the vent) is 22mm, the smallest pipe coming up from the bottom connection with the air vent on the top, (former cold feed), is 15mm.

Insulation get the thicker stuff, but please bear in mind, this is not a substitute for keeping the vulnerable areas warm in cold conditions. Insulation will help keep any warmth in the pipework, but wont prevent freezing if the temperature drops low enough.

Cylinder has sprayed on insulation, but it is the older type which is not as thick as the newer versions, adding a jacket (or 2) around it on top of what's there will not hurt anything, just ensure the stat is not covered.

Have you tried manually opening the HW valve to see if that is at fault?

 

[Mojo12345]

Hi thanks for the advice what’s the best thickness to wall of insulation I should get eg 19,25,32mm ? I’m looking at getting Armaflex it’s a bit more expensive, also do I insulate hot and cold pipes? Was looking at getting Armaflex insulation is it any good? Thank you

https://www.pipelagging.com/pipe-in...ulation-lagging-black-nitrile-foam-class-o-2m

 

[stem]

Originally you said that your issue was:

the hot water does not seem to be coming hot enough after the boiler has been switched on for an hour, the central heating works ok but the temperature of the hot water is Luke warm all around the house,

Then you posted a photo of a combi boiler which provides instantaneous hot water directly to the taps on demand, without a requirement for water storage....

....and a photo of a hot water cylinder

But you still haven't explained which one provides the hot water to the various outlets in your home. Is it the combi or the cylinder? Whilst it's possible that the hot water supply is split between the two it would be very unlikely. But you need to determine this before trying to resolve the issue with the lukewarm water.

 

[Mojo12345]

Is this a combi boiler? I thought it was a conventional boiler? Because it heats up the pipes, the pipes then go to the water cylinder? It doesn’t seem like a combi as I don’t get instantaneous water when the taps go on? Also if it was a combi boiler there wouldn’t be a water cylinder in the loft? I maybe be wrong but I don’t think it’s a combi boiler, what makes you think it’s a combi boiler? Thanks

 

[stem]

what makes you think it’s a combi boiler?

The controls on the front of it that are there to control the temperature of the water it is supplying directly to the taps....

....and the manual

I also suspect that the tanks in the loft may not be used anymore, but have been left there from an older installation. For example, I noticed that your boiler has a expansion vessel [Although I'm not too sure why it's there as I would have expected the boiler to have it built in]

An expansion vessel is used on a sealed system, so there is no need for a feed and expansion tank. ie This.....

 

[JohnD]

I also suspect that the tanks in the loft may not be used anymore, but have been left there from an older installation.

But he's got a yellow vented cylinder.

hence the big tank.

 

[stem]

Indeed, but it's rather unusual to have a combi and also hot water cylinder in use. I've seen installations where a new combi boiler has been installed the old tanks have just been abandoned. I did ask the OP on Wednesday to check, but they never replied.

First of all I would ascertain if the hot water cylinder is actually in use. It's quite easy to test. Switch off the central heating and whilst you stand near the boiler get someone to open up the taps one by one for 30 seconds or so. If the boiler fires up every time a tap is opened the boiler is providing the hot water and not the hot water cylinder. Are the cold water storage tanks above the hot water cylinder empty?

Of course, the combi may be feeding perhaps a single shower or the kitchen sink for example, whilst the hot water cylinder supplies the bathroom/s. But unless we're told who knows?

 

[Mojo12345]

Hmm confusing, I just left a hot water tap on for 5 minutes the boiler didn’t switch on or start working, the only time the boiler works is when the hive heating timer switches on the hot water, also the green hot water cylinder in the loft the pipes get luke warm when the boiler is on, but the thermostat clicks at 40 doesn’t got to 60 which I believe is the recommended, confusing

 

[JohnD]

the only time the boiler works is when the hive heating timer switches on the hot water,

ah, he's got a Hive.

What's the single most common cause of problems on P&CH?

 

[stem]

Indeed. I think you need to get it inspected by a professional to find out what's actually going on, it's an odd installation by many accounts. Do both of the cold water storage tanks above the hot water cylinder contain water?

 

[Mojo12345]

Yes the 2 tanks in the loft contain water and the top pipe coming out of the hot water cylinder gets warm, could it be possible that the previous owner had a combi boiler fitted but it’s been installed to work like a conventional boiler? I shall try and take more pics tomorrow when I go in the loft